Search

Identification of suitable habitat for invasive weeds and their projected infestation extent across different land use cover types under a changing climate is crucial for the broad management goals of prevention, detection, and rapid response. In this study, we adopted an ensemble approach of species distribution models to project potential habitat of the invasive annual grass, Ventenata dubia, within the Gallatin County and along its road corridors, in Montana, USA, under current and future climates. The model prediction of V. dubia habitat was excellent with an AUC value of > 0.90. The climate predictors with most influence on V. dubia occurrence were precipitation, potential evapo-transpiration, relative humidity, vapor pressure deficit, and solar radiation for growing season months. Under current climate, the model projected 243 and 1,371 km2 coverage of V. dubia along road corridors and the entire County, respectively. The projected coverage of V. dubia was greatest for road corridors (239% under RCP4.5 and 302% under RCP8.5) compared to that of Gallatin County (127% under RCP4.5 and 241% under RCP8.5). Among the land use cover types, the model projected greatest expansion of V. dubia across agriculture land with 425% and 484%, and grasslands with 278% and 442% under RCP4.5 and RCP8.5 respectively. Our modelling approach suggests that the changing climate will facilitate spread and establishment of non-native species in disturbed habitats. We conclude that V. dubia with a short history of invasion is expanding at an alarming rate and requires greater investment in detection and monitoring to prevent further expansion. [ABSTRACT FROM AUTHOR]

In isolated islands with low pollinator diversity, it has been suggested that native pollinators should evolve into super-generalists that could facilitate the spread of exotic plant species that might otherwise rely on specialist pollinators. Consequently, in the absence of exotic pollinators isolated islands may still be particularly vulnerable to a wide variety of introduced plants. Fiji has a highly abundant and diverse introduced plant fauna, as well as a variety of introduced bee species, but has extremely low endemic bee fauna diversity. We examined bee–plant pollination networks in lowland regions of Viti Levu (Fiji) where there is only one endemic bee species, Homalictus fijiensis. We show that this bee is a super-generalist for introduced plants, and whilst introduced bee species can show high intensities of floral visits, they do not substantially increase the breadth of weeds receiving bee visits. Surprisingly, one introduced plant species, Sphagneticola trilobata, receives high visitations from introduced bee species, even though it spreads vegetatively. We regard this species as a 'Parlourmaid' weed that likely augments the spread of exotic bees without gaining pollination benefits. Our results indicate a 'twofold' promotion of invasive species, namely, super-generalist native pollinators can promote the spread of diverse introduced plants, and Parlourmaid plants provide resources that can promote the spread of introduced pollinators. [ABSTRACT FROM AUTHOR]

Introduced weeds are hypothesized to be invasive in their exotic ranges due to release from natural enemies. Cirsium arvense (Californian, Canada, or creeping thistle) is a weed of Eurasian origin that was inadvertently introduced to New Zealand (NZ), where it is presently one of the worst invasive weeds. We tested the 'enemy release hypothesis' (ERH) by establishing natural enemy exclusion plots in both the native (Europe) and introduced (NZ) ranges of C. arvense. We followed the development and fate of individually labelled shoots and recorded recruitment of new shoots into the population over two years. Natural enemy exclusion had minimal impact on shoot height and relative growth rate in either range. However, natural enemies did have a significant effect on shoot population growth and development in the native range, supporting the ERH. In year one, exclusion of insect herbivores increased mean population growth by 2.1-3.6 shoots m, and in year two exclusion of pathogens increased mean population growth by 2.7-4.1 shoots m. Exclusion of insect herbivores in the native range also increased the probability of shoots developing from the budding to the reproductive growth stage by 4.0× in the first year, and 13.4× in the second year; but exclusion of pathogens had no effect on shoot development in either year. In accordance with the ERH, exclusion of insect herbivores and pathogens did not benefit shoot development or population growth in the introduced range. In either range, we found no evidence for an additive benefit of dual exclusion of insects and pathogens, and in no case was there an interaction between insect and pathogen exclusion. This study further demonstrates the value of conducting manipulative experiments in the native and introduced ranges of an invasive plant to elucidate invasion mechanisms. [ABSTRACT FROM AUTHOR]